Graduate Thesis Or Dissertation
 

Development and validation of acoustic measurement techniques for void fraction in concentric annular geometries

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rj430d005

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  • This work investigates the acoustic velocity of gas-liquid mixtures in vertical, co-current flow in a concentric annulus. Acoustic velocity shows promise as a detection parameter for the presence and amount of gas in a liquid flow because of its high sensitivity to gas void fraction in a gas-liquid mixture. However, multiple acoustic propagation models exist (e.g., Wood’s Homogeneous Model and Effective Medium Theory), which fundamentally differ in their prediction of the acoustic velocity of gas-liquid mixture. It is not known which model accurately describes the acoustic velocity in an annulus. Thus, in this study, acoustic velocity was measured for gas-liquid flows in a concentric annulus constructed of a transparent 4” outer pipe and an opaque 1” inner pipe. The gas mass flowrates ranged from 0 kg hr-1 to 1.0 kg hr-1, corresponding to gas void fractions ranging from 0% to approximately 12%. The liquid phase flow conditions were 0 gallons min-1 (GPM) and 1 GPM. Pulse and continuous wave acoustic measurement signals were generated using an underwater loudspeaker immersed in the test medium at frequencies of 500 Hz, 1 kHz, 2 kHz, and 4 kHz to measure the acoustic velocity. Research on conventional leak detection in petroleum wells has shown that current leak detection techniques are uncertain, limited in their availability, and slow to detect leaks. Research has suggested using downhole acoustic measurements to provide faster and more certain leak detection, as well as a quantitative estimate of the leak’s gas void fraction. Because the well drilling process involves an annular configuration, an emphasis was placed on acoustic and pressure wave measurements of gas-liquid flow in pipes and tubes. Bubble resonance was revealed to be a critical phenomenon involving acoustic velocity measurements of gas-liquid flows. Bubble resonance is a wave produced by bubble pulsation which attenuates acoustic waves to the extent that it could completely destroy a measurement signal. A bubble’s resonance frequency is inversely proportional to its diameter. Because the bubble size associated with a gas leak in a well is unknown, it was important to evaluate the potential effects of resonance on an acoustic measurement scheme. A review of the literature on acoustic measurements of gas-liquid flows revealed one investigation that measured near the bubble resonance frequency, which used a measurement signal that could not be implemented in a wellbore. Bubble sizes in this work were evaluated by direct observation of video and photographic recordings of the test section during experiments. The majority of bubble sizes in the populations generated during experiments ranged from approximately 1/8” to 3/8”, corresponding to resonance frequencies ranging from approximately 2100 Hz to 750 Hz, respectively. Thus, measurements made during these experiments were made at frequencies that passed through the resonance frequency band. The acoustic velocity measurements made in this work showed agreement with Wood’s Homogeneous Model, which is frequency-independent, suggesting that the measured acoustic velocity is not dependent on the measurement signal frequency. The outcome of this work permits implementation of Wood’s Homogeneous Model in an acoustic detection scheme.
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  • Pending Publication
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  • 2023-09-21 to 2024-04-22

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